In recent years, photocatalysts has been recognized as a desirable technology for chemical synthesis and chemical degradation such as air and water purification, anti-bacterial applications, self-cleaning coatings, and deodorization etc. Titanium dioxide is a photocatalyst which is active under ultraviolet (UV) light. Titanium dioxide (TiO2) has been of particular interest due to its low cost, almost no toxicity, chemical stability (both to light and the environment) and high photo activity. A large number of prior state of the art references have mentioned using titanium dioxide as a photocatalyst.
TiO2 has been used in a wide range of applications including ultraviolet filters for optics and packing materials, environmental remediation, papermaking, ceramics, solar cells, electro-chromic displays, anodes for ion batteries, self-cleaning coatings and paints and humidity as well as gas sensors.
Since titanium dioxide of the anatase type or rutile type has a band gap of 3.2 eV (corresponding to a wavelength of 387.5 nm) or 3.0 eV (corresponding to a wavelength of 413.3 nm), respectively, only UV light having wavelength of less than 387 nm can be utilized for its activation, and visible light (380 to 700 nm) cannot be utilized at all. Titanium dioxide is difficult to be utilized in the applications of interior paints, textiles and sick house syndrome alleviating agents that are used in a room where substantially no UV light exists. While functional under UV irradiation, photo-catalysis generally does not occur in indoor areas under conventional artificial light or even ambient daylight as UV is not present and the application of titanium dioxide has been restricted in actuality.
Many attempts have been made to modify the photocatalytic activity by doping titanium dioxide with a number of different compounds and using a number of different techniques. Several different nitrogen-containing compounds have been tried using a variety of different doping reactions. Also, a number of attempts have been made to modify TiO2 to enhance its activity by doping the crystalline structure with a variety of compounds including those with carbon or sulfur atoms. However, these attempts have limited stability and efficiency or were active only or primarily under UV light.
Some attempts have been made to obtain visible light activation of the photocatalyst by the red shift of the absorption spectrum. Nitrogen doping and silver doping have been effective in decreasing the band gap of TiO2. Various methods include photo deposition, chemical reduction, liquid impregnation, deposition-precipitation, sonochemical synthesis etc. Most of these processes require long synthesis time and sometimes calcination for removal of undesired products on the surface of titania.
Mechanochemical method has recently become a promising technology for doping on titania.
Aysin et al (in Brno, Czech Republic, EU, 21.-23.9.2011 reported photocatalytic efficiency of silver loaded nano-sized photocatalytic titania powder prepared by ball milling of photocatalytic titania powder (anatase), with 0.1 M silver nitrate solution and 1% sodium carbonate solution. Photocatalytic performance was evaluated under UV light illumination. It was observed that though the silver loading enhances the photocatalytic activity, as amount of silver loading increased, the photocatalytic activity of doped titania powder decreased.
Ramida Rattanakam et al in Res Chem Intermed (2009) 35: 263-269 reported preparation of N-doped TiO2 by a mechanochemical method using high-speed ball milling of P25 TiO2 with nitrogen source such as ammonia solution, hexamine and urea. The photocatalytic activity of the N-doped TiO2 was evaluated under sunlight irradiation. The results indicated a slight anatase to rutile phase transformation during the mechanochemical process. It was observed that the photocatalytic activity of the doped titania particles was not improved as compared to the starting P25.
In a co-pending patent application 1224/MUM/2012, which is the priority of later filed U.S. patent application Ser. No. 13/861,643 filed on Apr. 12, 2013 published as U.S. Patent Application Publication No. 2013/0274091 on Oct. 17, 2013 and which issued as U.S. Pat. No. 9,006,124 on Apr. 14, 2015 which is incorporated herein by reference, silver doped titania having photocatalytic activity greater than 90% in 3 hrs under sunlight irradiation, is developed using a mechanochemical method. However, the document does not disclose photocatalytic effectiveness of the doped titania using ambient light, particularly in poorly illuminated areas.
Therefore, there is felt a need to develop a suitable doped titania photocatalyst which shows higher photocatalytic activity under visible or artificial light irradiation.
Objects
It is an object of the present disclosure to provide a doped titania having high photocatalytic activity under visible or artificial light irradiation.
Another object of the present disclosure is to provide a feasible process for preparing visible light responsive doped titania photocatalyst.